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Jim's Crazy Bio-Filter


OK. This page is where I show you how I built my own homemade bio-filter based upon a "Skippy" filter. There are a lot of pictures on this page so be please be patient while it loads. By now you've (probably!) read the Introduction page, and the Design Considerations page.

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Let's Build It!

You should consider as we go that this was how I built a bio-filter for my pond. Assuming you are attempting a DIY approach you will obviously need to adapt it to your situation.

I already had a small filter (Hozelock Cyprio Bio-Force 2200 UVC), and a pump (Hozelock Cyprio Cascade 4000).

I also wanted the water coming out of the filters to go into the back of the terracotta urn (via pipes going into holes I drilled in the back of the clay urn), spill out of the mouth of the urn, down the waterfall and the stream.

So consider your own needs, and plan accordingly. I find this works for my size of pond (400 gallons), but you may need to upsize!


The Big Search

A key factor in my minds eye was to use a big plastic flower pot, which should look nicer than a big black Rubbermaid tank so typically used for a Skippy style filter - not so obtrusive, would be easy to drill holes in, and a cylinder contains more volume than a square or rectangular tank of similar size. And as mentioned previously water swirls inside it more naturally. So I visited a couple of garden centres to see what I could find.

Nice, but not good enough!
Hmm. Nice big pot.....

....but the patterning would be awkward to drill through and create a waterproof seal.
A bigger better pot
An even bigger pot. More like the size I want......
This pot is about 47cm across the top.
...and the patterning has enough space around to allow drilling and the water outlets to sit flush.
It leaks!
Another pot, but smaller, and it had extrusions with holes in the bottom making it useless to hold water in.
Looking down inside the pot, with a sieve which matches perfectly
Excellent, I have also found a plastic sieve which fitted perfectly in the bottom of my chosen pot which the filter media would sit on top of, thereby creating a gap for the water vortex underneath.



Basically I now simply needed a variety of pipe fittings, clips and hoses to work with:-

All the bits n bobs

  • Big pot 47cm diameter across the top (£20)
  • 25mm Flexible hose (in fact the black hose shown here was very stiff, and didn't get used in the end, £6 wasted! I got some other more flexible hose later on 2m of 40mm hose to exit the filter, and 3m of 25mm to enter the bio-filter)
  • Plastic sieve (£2.50)
  • 40mm U-Bend piping kit (all necessary rubber seals, and fittings included, £5)

A closer look, jubilee clips, T-pieces, bends, shower drain unit and piping

  • 40mm Shower drain unit (one of the more expensive items £10)
  • 25mm black double-ended hose connector (£4, I got this to join existing piping at my Bio-Force UVC filter when I excluded it from the loop. In fact I put the Bio-Force back in as a solids pre-filter, so this connector was not used after all)
  • 3 x 22mm pipe right-angle bends, push fit (99p each)
  • 2 x 22mm pipe T-pieces, push fit (99p each)
  • 1 x 22mm pipe tank inlet, straight-through (£1.25)
  • 2 x 22mm pipe tank overflow, right-angle bends (£1.25 each) NB. one of these was later replaced with a 40mm tank outlet, see below.
  • 4 x 18-30mm metal screw-adjust "Jubilee" hose clips (50p each pack)
  • 22mm plastic water pipe, 2m length (£1.50)
  • Also (not pictured),
    • A pack of Pond Bacteria culture to help start maturing filter,
    • a 40mm tank overflow outlet (I used this to replace one of the 22mm ones later on to ensure good exit flow from the bio-filter back to the pond)
    • Fernox LS-X jointing compound and leak sealer glue (dries rubbery, acetic acid (vinegar) base which cures on contact with water)
      Fernox LS-X plumbers jointing compound - Glue!


Starting Work....

The shower-drain unit by coincidence matched exactly the size of the recess in the bottom of the pot.....

Using a drill of the right size to match the shower-unit, drill through the base.

Pilot hole first....
Drill nice n easy, with firm pressure
...then main hole.

A perfect fit. See notes about sealing this with plumbers jointing compound later on. Extremely important.
See that 6 spoked plug hole centre? You can take it out, so I removed it to give better drainage otherwise it blocks up all the time.



Inlet & Overflows

Consider the angles of where you want your pipework to enter and exit the bio-filter, i.e. where are your pump, pre-filter, and returns back to the pond located? This should dictate the orientation of your bio-filter tank, how the pipes come to it, and where you intend to put buckets/watering-cans when emptying the filter, or even where the waste water will go to if you're just emptying straight onto the ground. Plan and mark out where you want the inlets and outlets to go. In my case I found that this was partly dictated by the raised flower pattern decoration on the sides of the big pot, because I had to drill in between on the flat parts.

Now drill and fit the inlet and overflows.

I would recommend not doing things up too tight or sealing them during the experimental stage to allow for adjustments to be made. I created 2 overflows because I knew that my pump would force more water into the tank under pressure than would be allowed out under gravity. In fact, much later on I replaced one of the 22mm outlets with a much larger bore 40mm outlet and flexible hose, which works much better at letting the water out. I was concerned about these narrow 22mm pipes becoming blocked and causing the bio-filter to overflow, so losing all the water from the pond with potentially disastrous consequences!!!

A jubilee clip is essential to ensure secure fitting of pipe to outlet.
Drill to accomodate the 22mm pipe fittings for the one inlet and the two overflows. Notice how I had to fit it between the raised decorative pattern to ensure a flush fit.

I experimented with angling the pipe of the overflows to determine the water-level inside the filter. Later, after final assembly, I took them all out again, applied a generous helping of Fernox jointing compound to the inside and outside faces, and the flexible hoses before re-fitting. This gave a totally watertight fit with no leaks!

A jubilee clip ensures the pipe won't get knocked off.
This is the 40mm outlet and piping which I used later on....
(notice the jointing compound to seal the join).
This pipe feeds off into a large hole carefully drilled into the back of the terracotta urn, which sits at the top of the waterfall.

This larger 40mm outlet has much better capacity
to let the water flow out.


Main Flush Drain

Next task was to fit the shower-drain unit, and measure and cut the pipework to create my main drain outlet. My idea was to have the pipe clipped against the side of the tank. I lubricated the rubber seals for the pipework with vaseline, not only to provide a good watertight seal, but also to allow the whole pipework to be unclipped, and rotated easily to allow emptying of the filter. I figured that pipe of this bore would allow the water to exit rapidly, so dragging any muck out quickly. In practice this works a treat, and allows a very quick cleanout every day or 2, taking no longer than 30 seconds, dumping into a watering can, and the pump still running. Easy maintenance!

The length of the pipe allows me to lower it over a watering-can which can then be used to water plants around the garden, or to fill up a bucket for cleaning of the pre-filter media or the bio-filter media. And also because the top of the pipe is open, I can put new Bacteria Culture into the top, and literally "inject" the bacteria right into the heart of the filter, by pouring pond water in to the pipe. All will become clear!

Another thing to mention is that the shower drain has a 6-spoke plughole centre (see earlier picture). It is possible to remove this, and its shower trap shaft. This would normally form the trap for any hair and muck which normally goes down a plug hole, but I found that this just got blocked up with sediment or any algae/blanket-weed so I removed it altogether. This improves draining the bio-filter quite substantially, and also allows a clearer passageway for sediment to drift down into the main body of the trap during the day, ready to be flushed out the next time I clean it.

Note that due to the protrusion of the shower-drain unit and pipework at the base of the tank it is necessary to have a sturdy platform to straddle each side of it, and support the weight of the tank and water. This is achieved very nicely by two house bricks sat on top of a level paving slab, which give a solid sturdy base. When the tank is filled with water it is very heavy!

A good view of the shower trap drain unit..

The main drain assembled. The point of rotation of the P-trap (the part I am holding in the above photo) is on the axis where the pipe goes into the shower-drain unit. I unclip the pipe from the side of the tank, and pivot it left and down. The water will then flow out of the main riser pipe (see pictures near bottom of this page in the Cleaning the Bio-Filter section, also note in those pictures that I have flipped the P-trap the other way around). The P-trap allows me to rotate the drain downward to empty the bio-filter into a waiting bucket. I smear some vaseline on the rubber grommet in the P-trap so it will rotate easily. I suppose instead of a P-trap it could have been just a normal 90 degree bend, but my thinking was that the P-trap bend may provide some additional room for sediment to settle down into, ready for when I flush it out. Also it came as part of the pipework kit I bought from the store so it seemed to make sense to make use of it.

Sat atop two garden chairs while testing.

The tank is now filled with water as a test to see whats leaking!

Hmm. Plenty! A leak is not good here. Again while I was still constructing the whole thing I didn't worry too much about sealing, but once I had the design and any tweaking done, I used some Fernox plumbers jointing compound. This is wierd stuff which is clear, smells of vinegar (because it uses acetic acid to help the curing process), and sets on contact with water. It doesn't seem to hurt your skin so even though its not pleasant I used my fingers to spread it over the surfaces - I used plenty - rather be sure than sorry. Keep it away from your eyes though, and wash your hands well after using it!

When set it is rubbery and pliable, and creates a very good seal. I paid a lot of attention to making sure the shower-drain unit, and the main drain pipework were very tight and well sealed, either with Fernox where I didn't want it moving, or with vaseline where I intend the whole pipe structure to rotate when emptying the filter.

Note also that I used the Fernox on the inside where the nut & bolt are holding the pipe clip to the tank, to make it both watertight, and help prevent corrosion.

There is one thing I am wondering about with my design. Whether there is a risk of the bottom drain/u-bend freezing in winter, and expanding so causing leakage, or at worst total flood-out of the pond. Hmmmm!? Perhaps there won't be a need to run the bio-filter in winter for my size of pond and fish? Or perhaps the constant flow of water will keep it from freezing? This is something I will have to keep a cautious eye on.

Update: I had no problems this winter just gone, even with the top of the pond actually freezing over. This is a British winter though! Mild compared to some countries.

The pot holds about 12 gallons of water.

Obviously the water level in the tank also rises in the pipe on the outside, so the length of the rising pipe must be sufficient to always be above the maximum expected level of water inside the tank, otherwise it would overflow from the top of the up-pipe! Not what you want!

At this stage I found that there was some natural give and droop in the pipework due to the rubber seals, and the added weight of the water in the pipe, which the plastic clip holding the pipe against the tank could not support. To cure this I added a couple of screws to help hold the pipe up on the topside of the clip. See below. At the time I kicked myself for not cutting the pipe longer, but in practice there is just sufficient height for it not to overflow. The water goes out of the proper outlets as intended.

Update: I have since replaced this pipe with a much longer section, that now comes about 10cm above the top of the bio-filter pot. What I have found is that when the pump is forcing water down into the vortex chamber section at the base of the filter, there is a slightly increased water pressure which results in this drain pipe having a slightly higher water-level. It is much better to have too much height of pipe than too little.



Settlement Chamber Vortex Swirler

Note that this build section was modified later on when I added the venturi. Please read the whole project construction process before starting to cut any pipework! (Unless you don't want to build the venturi).

My theory for the vortex settlement chamber was based on the idea proposed by the Skippy Filter, where the water is fed to the bottom of the filter under pressure and out of two pipes in opposing directions to create a circular swirling vortex motion. The idea being that:-

  • its better to keep muck out of the bio-filter, so this settlement chamber hopefully catches anything let through by the pre-filter
  • the water is distributed evenly around the vortex settlement chamber before moving upward through the garden sieve and the filter media
  • a whirlpool or vortex action causes muck and sediment to move to the centre and settle downward into the drain unit ready for expulsion when the filter is emptied

This is the basic layout - a down pipe goes into a T-piece, then outward to the right-angle bends to create a clockwise motion of the water.

The opposing pipes cause a water vortex or whirlpool that draws sediment to the middle where gravity will drag it down into the shower trap.

Here is the swirler measured, cut and assembled. Note the slight downward angle at each end to help move sediment to the floor of the chamber.

Now get the sieve. Fairly ordinary. 36cm diameter.

With the lucky combination of this size of sieve and the diameter of the main tank, when the sieve is placed in the tank as far down as it will go and rests on the sides, there is still about a 2 inch gap between the bottom of the sieve and the floor of the tank for the vortex.

Cut out a segment from the centre of the sieve. This segment, I found out once again by chance, was a very snug fit for 22mm pipe to pass through. How lucky am I?

I used wire clippers to snap out the central square to allow the piping thru.

And now the swirler can be put in place through the sieve. The T-piece fits nicely against the bottom of the sieve without going through the cut-out segment.

Note in the picture below that the top of the swirler is against the bottom of the sieve, with about a one and half-inch gap from its underside to the bottom of the tank.

Next put the swirler/sieve assembly into the tank and measure the rising pipe length to the pump/pre-filter flow inlet flange.

After cutting the pipe, put a right-angle bend on the top.....

Then measure and cut the pipe for the feed from inlet to the down-pipe, and fit in place......

Simple but effective....!

Some more testing to see how it all works, check water levels, overflows, and swirler action.

So far so good! Although I'm a bit dubious about the very stiff black pipe I've got. Think I need to get something more flexible.

During testing and filling, I discovered that air trapped under the top lip of the sieve was sufficient to cause it to float upward, so I drilled several holes around its circumference. Not too many because I want the majority of the water to be channelled up mainly through the bottom of the sieve, not through the holes at the outer side of the sieve.



Final Assembly

Finally all that is required is to assemble everything, put the filter media in, start the pump and check for leaks.

Again I did a test run before securing everything, because once in place I found that there were several small leaks around the jubilee clips used to connect the hoses to the inlets and outlets. A good daub of Fernox plumbers glue fixed the leaks. Also note in this photo that I have fitted better flexible hosing (I think its called Flexihose) rather than the very stiff hose I got initially.

Once you are happy with everything, put the filter media in (see next section).


The Big Green Scrub-Up! (Filter Media)

Skippy's site recommends industrial size green nylon scrubbing pads for the filter media. Lots of people seem to use and recommend this stuff. Despite its rather innocent normal purpose, it has a high surface to volume ratio of 300:1 making it a very good surface for bacteria to colonise.

It was quite hard to find a supplier of the big thick pads. I did not use the circular pads used on floor cleaning machines. They were quite expensive, and I needed quite a lot. A friend offered me a whole load of these free, but they had been used and though he cleans them afterwards I was concerned that they would contain floor cleaners and traces of dirt that would either prevent the bacteria growing, or worse could poison my fish!

It amazed me how much people charge for this stuff! Normally housewives buy this from their supermarket in a little pack of 5 for their housework and it lasts them a few months, so they don't mind paying a couple of quid. Skippys supply it in bulk at a very reasonable price, but they are based in the USA.

After much searching I found a reputable Internet company in Scotland called Scobies Direct who are suppliers to the butchers trade. Butchers have to clean their work surfaces very regularly, so Scobies supply these large size scrubbers in bulk.

I ordered 1 box of 120 pads which was plenty for the task (and still I had about 50 pads leftover)

It arrived 2 days later. These scouring pads are 230 x 150mm x 8mm (9 x 6 x 1/4 inch), designed for industrial use and are suitable for all cleaning applications - and ponds! Now if they are suitable for cleaning surfaces used for preparing meat on, then I think they will be alright for my fish! They probably aren't quite as thick as the ones supplied by Skippy's (which I think are more like 15mm), but they seem to be perfectly adequate for the job and are slightly thicker than the usual dishwashing green scouring pads (that supermarkets charge the earth for!!).

At Scobies just go to the Sundries, Disposables section where you will find them, or click this link:-

At the time they cost £14.95 for the box, the total order was about £23 after VAT and UK post & packing.

Update: Recently I was told that Scobies are having stocking issues with these pads. I am trying to find out more from Scobies currently, but in the meantime I have located an alternative stockist who charges a bit more. They are Akro Services and you can find their Green Scourer Scrubbies Pads (product F959 currently at £2.75 box of 10) by clicking here: http://www.akroservices.co.uk/products.php?cat=1082

Another supplier that I have been told about is Ace Janitorial Supplies Ltd in Sheffield, UK. (Tel: Paul Cullumbine on 0114 244 4474 or 0114 244 5035), Email: info@acejanitorial.co.uk, Web: www.acejanitorial.co.uk. They supply 9x6 inch contract scouring pads in boxes of 50 for £6.60 inc. VAT per box. A friend of mine who has a much larger pond, built two filters using two 80litre bins from his local B&Q store and based on my design. They feed one into the other for his 3000 gallon pond. He bought 10 boxes initially but later found that 6 boxes were sufficient for his two 80 litre bins.

Also thanks to Andy who let me know about this site:-


Pack of 20 for £2.99 inc VAT (multi colours too!!!)

To load the filter, I simply set the water running through the tank, so that I knew the top level to fill up to with the filter media. then simply set about cutting up the pads. They are good size pads, so most I cut into quarter size, while some I only cut in half. As they went in, I gently pushed them down to soak them, and get them to fill all the gaps nicely.

The idea with using these is that they create natural voids between them which the water can track between, so the filter won't become blocked by any solids which get through from the pre-filter. The intention of the media is to slow, not block, the passage of water through so as to maximise the time the water is in contact with the bacteria who make their home on each pad.

Once finished there was still a good flow of water through, which after exiting the filter still gave a nice gush of water from the terracotta urn, and down my stream.

I also cut a plastic carton to fit around the main overflow to prevent the pads from going over it and blocking it up.
It turned out that this wasn't really necessary, because once wet, the pads pretty much stay where they are put.


Friendly Bacteria

One thing I like about the main drain is that it can also act as an "inlet" to the filter.

To get the filter started I poured the contents of a packet of bacteria culture into the top of the main drain and then poured enough pond water (NOT tap water) into the pipe to flush the bacteria powder through into the heart of the filter (probably a gallon of water).

This was done while the pump was running and will help jump-start the new bacteria forming in the filter, and the pond. This can be repeated with some more perhaps 1 week later, according to the instructions provided with the bacteria, and thereafter probably on a monthly basis to ensure good strong growth of the bacteria throughout the year.

Click here for more information about Bacteria Cultures and products suitable for Bio-Filters.

Every Little Bit Helps

The box of 120 filter media I got from Scobies Direct had plenty of pads to fill the filter, and then some. I figured that I could extend the bacteria colony beyond the actual bio-filter.

Anaerobic bacteria live anywhere in the pond, in the silt, on stones, on the sides, on plant roots. The bio-filter is simply their main home.

So why not give them additional living quarters in the terracotta urn at the head of the waterfall?

So I simply cut up and added a stack of the scouring pads into the urn as well. This should mean there are even more bacteria available to purify the water.


Additional Tweaks


The photo below shows the Hozelock Cyprio Bio-Force 2200+UVC filter hiding under a curry-plant. Click here for the Hozelock Cyprio site. I mentioned on the Introduction page that I made the mistake of thinking a pre-filter wasn't necessary with a Skippy filter, and so for a couple of weeks I totally bypassed the Bio-Force filter (luckily I didn't remove it since I thought better not until I had tried things out).

Well after researching some more, like I said I learnt of other people saying their Skippy's were becoming very glooped up with cruddy slimy waste, and more knowledgable people saying its best to use a pre-filter to cut out as much of that solid fishy waste as possible. So I reconnected the Bio-Force back into place, and now when I do a cleaning dump on the main bio-filter, there is certainly not as much nasty looking gloop.

I just wish there was an easier way of cleaning the Bio-Force. I still needed to clean it out every 2 or 3 days because it gradually gets blocked up and the water slows to a trickle. While I'm quite used to doing it, it is a bit of a pain bending over, unclipping the top, removing the coarse and fine foam rings, cleaning them out thoroughly, and then putting them back, while also being careful to get the rubber sealing ring back in place without trapping it, or it dropping into the casing and having to open it up and retrieve it again! It's a fiddly job, and in winter can be a very cold job too!

The one consolation is that I know it is catching all that muck, and believe me, there is plenty.

Update for 2005

Do I still use a pre-filter / mechanical filter?

Yes, but I have now made my own DIY pre-filter (June 2005), and I have at last upgraded my pump to a Hozelock TITAN (see further below). But here is some history of how and why I decided to build my own design of Pre-Filter.....

Before I built my Skippy-style bio-filter initially I was using the Hozelock Bio-Force UVC filter. As you've read you'll realise that I was totally fed up with cleaning this out, especially in the summer, every 2 days because the water would absolutely STOP DEAD. It would get so blocked up with large and fine particles in the foam sponge that no water could get through at all!!

Basically the Bio-Force UVC 2200 filter was not man enough for my pond, even though its a small pond! The ultra-violet light certainly seemed more of a gimmick than anything because it never helped my green-water problems, and the foam filters in the unit just clogged up too quickly. Bacteria NEVER got a chance to breed or work in this manufactured filter and there was never enough surface area for any bacteria to cope with even my small pond. It was just too small and I was cleaning it out too regularly.

Cleaning the Hozelock filter out was time-consuming, messy, cold and fiddly. Turn off the pump, unclip all the clips on the top, lift up the top carefully making sure not to bend the pipes too much (which invariably created leaks), squeeze out the foam filters (cold, wet, not fun), then put it all back together, making sure the rubber seal was seated correctly (which one time when we went on holiday and my neighbour was left in charge, he didn't do properly and the pond nearly emptied dry!!), then re-clip the clips (which are quite tough to snap back into place, and one clip broke off).

Anyway, when I had first completed my DIY bio-filter, I decided (like you are probably also wondering) to keep the Bio-force UVC filter plumbed in just before my Skippy bio-filter. So this was pre-filtering the muck before the bio-filter, which meant I STILL had to clean it out every couple of days!

Now on the Skippy web site, they say that they don't use a pre-filter as such. I emailed them about this, and they said that the plastic or wire cage surrounding the pump in the pond is usually sufficient.

Well time went by, and this winter just gone, one day when I was cleaning the Bio-Force filter, the plastic flexible hose leading into it "gave up". It was brittle in the winter cold, and had been bent too many times by me lifting the lid of the filter off.

So I had no choice! The pipe was now too short to lead into the Bio-Force unit, and it was too cold and I was too lazy to repair it properly (I would need to dig up a considerable part of the the rockery to get to the pipe, refit a new one, and re-plumb it in). So instead I went for a quick fix and cut and re-joined the pipe directly to the Skippy, so omitting the Bio-Force UVC filter altogether.

For several months my DIY bio-filter had been operating without a mechanical pre-filter other than the plastic cage that surrounds the pump in the main pond (and which you will read further below, I had drilled a whole load of extra holes in the cage to allow water and muck to pass through more easily).

IMPORTANT: If you read my Design section about the theory of the bio-filter, I explain that you get two types of bacteria aerobic and anaerobic. The aerobic bacteria are the good ones that really help the digestive process of the bio-filter, just like a sewage farm. Anaerobic is what results in stagnant still water, and you do NOT want that kind. Anaerobic (bad) bacteria might be more likely to occur without a pre-filter because it might allow more fish poop to accumulate in the bio-filter.

Now sewage farms use huge pumps and mixers to pump air into the sewage before it goes into the filter beds. So I decided to use the same principle by adding a homemade Venturi at the top of my bio-filter. It sucks air into the water, creating bubbles which mix oxygen in, get passed down into the heart of the bio-filter, then bubble up and out. I believe that this really helps a lot. The waste solids can sink to the bottom for flushing out, and anaerobic bacteria doesn't get a chance to develop because 24 hours a day oxygen is being dissolved into the water and passed through the filter so encouraging mostly aerobic bacteria to develop.

So for the early poart of 2005 it all seems fine. Yes I am getting some algae and blanket weed while the pond develops its biological cycle, but the water itself is clear as anything, even though it gets a good deal of sunshine. I shall have to wait until summer to see how well it all copes. But I am confident. [Update Nov 2005: At the very height of summer I got some green water, and even then only after I cleaned the bio-filter a little too excessively which disrupted its biological process, but never has the green water been as terribly bad as it had been in 2004].

Also note that I have stuck by my word of not using any other kind of commercially available chemicals to treat the water. This is a totally natural system. The only thing I do is boost the bacteria by injecting some into the Skippy. Oh and make sure to use plenty of water plants too which help the balance and eat up extra nitrogen.

Re-Arranging the Filter Media

This year (2005) I have tried something different. At the start of the year I gave the bio-filter a total clean. This is ok because it was still the cold time of year when the bacteria are likely to be dead anyway. When I put the green scouring pads back into the filter I laid them carefully in a spiraling arrangement. Whereas previously I had just chucked all the pads in, this time my thinking is to close the gaps up, making its filtering process more efficient, and to also encourage a slow rotating motion of the water as it passes up through the filter pads. I made sure the direction of the rotation was also the same as that setup by the swirler pipes in the bottom of the bio-filter.

By laying the filter media pads carefully in this fashion you are able to fit a lot more media into the bio-filter. This means there is more surface area for bacteria to colonise, and more bacteria means more efficient cleansing of pollutants.

These are the old, rectangular scrubbies after cleaning, being laid in a spiralling, overlapping layout.

And similarly in the centre, always overlapping in the same direction.

Finally I cut diagonally shaped scrubbies for the last couple of layers at the top.

Here are the diagonal cut scrubbies in place, and all ready to go.

And this is after about 3 months. The bacteria has built up nicely in the bio-filter, and as you can see there is algae growing on the top where it is exposed to sunlight (this is ok and to be expected). I still haven't put plants in the top yet. I keep meaning to so that the big bio-filter pot looks as if its just a plant pot, but I guess I just like fiddling with it too much! Also notice my new Zik-style venturi in the top which draws air down to aerate the water before it goes into the bio-filter. This extra air oxygenates the water so that the "good" bacteria can live and breed and do their stuff on all the waste matter in the bio-filter.

Pump Modding

A big mistake I made, and would strongly advise other newbies to pay attention to is to make sure you buy an appropriately sized pump that is adequate not just for its immediate, but also future needs.

I have now (April 2005) purchased a Hozelock Titan 8000 litres/hour solids handling pump, but again here follows some history of my learning process.....

The Hozelock Cyprio "Cascade" pumps are really intended for small fountains and waterfalls. Granted that is what I have, and to be fair it suited the purpose at the outset, but now I've crossed the threshold from requiring a pump with a fine filter cage, to needing one capable of pumping solids, i.e. something more like the "Titan" range of pumps.

So whats the difference?

Cascade vs. Titan

Well, the "Cascade" has a plastic casing around the pump impeller that prevents solids going up the tube to the fountain spray, because without this the fine holes of the fountain spray-head would block very quickly. The pic below shows the surround casing after removal from the pump motor (which enables it to be cleaned). As you can see the slots are reasonably fine, each one is about 2mm wide, by 15mm long. They are intended to keep out solids; fish waste, bits of leaves, algae, blanket weed, etc. Which they do! But it tends to clog up so much that eventually the flow of water is inhibited. Then you have to lift it out of the pond and clean it.

If your pond has a fair bit of muck, and the fish constantly stir it up, then the cage could block up within 3 or 4 days. Maybe if you are using it to power just a fountain spray head which does not require much pressure then it would last quite a while. However for my purpose, since I need a reasonable throughput of water, the reduction in pressure soon tells.

Due to the evolution of my pond, I now need to push those solid wastes out of the pond, and my Cascade blocks up too quickly. I was having to remove the actual Cascade pump unit from the pond every 3 or 4 days, let alone clean out the Bio-Force filter every couple of days!

So I studied diagrams of the Titan pumps, and looked at the spare impellers sold in my local garden centre and compared ones for the Cascade, with ones for the Titan (shown here).

I identified the following differences:-

  • The Titan has a larger cylindrical filter cage around the pump unit. This larger area will allow a more even continuous flow of water into the cage, even when covered with a layer of blanket weed.
  • The Titan is advertised as being "eco-friendly" with a Wild Life Protection System (WPS). What this actually means is that there is a secondary cage at the base of the unit with sliding slots (look at the very bottom of the photo). When fully open these slots are about 10mm wide by 25mm high, but can be closed down to 2mm in the spring to prevent small critters being sucked up to an untimely demise! The lever to the left of centre in the above photo is used to adjust the slot size.
  • The slots on the Titan are at the very base of the pump which therefore is able to draw muck directly from the floor of the pond. This is much better for the health of the pond, because silt settles to the pond bottom where the pump can extract it.
  • The impeller that actually does the pumping is identical for both the Cascade and the Titan, but for one thing. On the Cascade impeller there is a sort of cap, which presumably helps make the impeller more efficient because it "draws" the water better. On the Titan impeller this cap is missing, which means that larger solids won't get caught/trapped in the impeller device.

The Cascade 4000 impeller has a cap over the impellor vanes. Water is drawn in from the front (left-hand side of photo), and pushed out of the sides. It's not intended for solids like stones, snail shells, leaves, etc, which could get trapped inside the cap.

The Titan 2000 and 3000 impeller is the same, but without the cap. Note the little lugs on the vanes which the cap would fit on if included. Ok, its green too: Green = Titan!
The Titan 5500 is however considerably larger and different.

Having spent the best part of £140 now on two pumps, the first rated at 2000litres/hour (440gallons/hour), and the second at 4000litres/hour (880gph), I now know I would have been far better obtaining a slightly higher rated Titan with solids handling capability (perhaps the 5500litres/hour model) right from the start. [I go into the power aspect a little more on the Venturi page].

My advice - don't just go for power. Consider the additional function of the pump for your purposes.

What do I do? Until I can afford a Titan, I'm going to be a tight old cheapskate and modify my Cascade to emulate the Titan in "summer" mode.

Or in plain speaking terms, I am going to get out the cage from my old Cascade 2000 (its exactly the same size as the Cascade 4000), and butcher it by drilling quite a few extra 8mm holes all around the base so that it can draw in solids and more water from the bottom. This photo shows the bottom of the cage before and after drilling the holes. The drilled cage will be my Summer pump filter, and the original cage will be my Winter/Spring pump filter.

Before drilling.... ...after drilling

How effective was it? Well even the larger holes still block up over time, but I have effectively increased the amount of inlet space/surface area to feed into the pump. The length of time between cage cleans has now extended to about 2-4 weeks. That'll do for me at least until I can afford a new Titan 5500 (another £130!). And if something like a stone or snail shell gets trapped under the Cascade impeller cap, I will simply remove the cap as for a Titan impeller, and see if there is any reduction in power.

[Sub-note: Stuff did start getting stuck in the impellor cap, and because it was getting quite old and worn I removed the cap from the impellor. The main wear on the impellor was due to a small bush which got lost during one of its routine cleanouts, which allowed the impellor cap to move too close to the impellor housing which it then hit against and started to crack the impellor cap. The damage was not as a result of stones or snails, they would just get stuck in the impellor and probably reduce its efficiency. I bet those snails got dizzy! Anyway there was only a very slight reduction in the power after removing the cap.]

Also available apparently is a Block Filter Extension. This is a block of foam which can be attached to the front end of the Cascade pump as a pump pre-filter. I am sure this would probably be yet more ineffective expense which would get blocked up!

Disclaimer: You will in all likelihood invalidate your warranty if you perform such butchery to your pump cage!


On the Bog

The next thing to fix up is the bog-area of the stream. If you remember, like fools we had removed all the overgrown Water-Musk. So we got some new clumps of Common Reed or Norfolk Reed (Phragmites australis) which is a top performer because not only has it got a phenomenal growth rate in the right conditions (don't get too many!!!), but it also oxygenates the water; essential for many of the bacteria that need oxygen to sustain them.

Here we have re-planted the reeds, and some other varieties of plants to get our natural "vegetable filter" going again.

Before new planting...

...and after.


Cleaning the Bio-Filter

Change Your Attitude

Part of the approach to achieving a healthy pond is to appreciate the way nature works. In the beginning my own mental approach was wrong. I wanted longer times between cleaning the filter, and was getting annoyed at how often I was having to clean the pre-filter.

Now that I understand the complete life-cycle in a pond, my attitude has changed and I now appreciate the importance of cleaning the filter system before it gets blocked up, and before the solids start to decompose.

I also now accept that in any filtration system, regardless of size it is a simple basic fact that the pre-filter would not be doing its job if it didn't become blocked up. I have switched my thinking from one of becoming annoyed at the prospect of regular cleaning being a chore, to that of enjoying the knowledge that I personally play a vital part in the chain of events that helps to make my pond clean and healthy.

So what needs to be done?

Every 2 to 4 days I clean the filter system (this takes between just 2 and 5 minutes of my time). 2 months after I finished my project I still clean the pre-filter every 2 or 3 days due to my changed attitude, although I have found that now that I have clear water I can in fact sometimes leave it for a week without cleaning.

The Skippy site says NEVER to clean the bio-filter media itself - LEAVE IT ALONE!

I have yet to see whether this is practical, but I intend to keep to their advice (Update: I dismantle and totally clean the bio-filter once a year just after winter). The only cleaning I will be doing is to flush out the settlement chamber using the main drain pipe every couple of days. (On this note one other modification I might make is to add either a manual valve, or automatic non-return valve to prevent the water syphoning back into the pond when I turn off the pump - Stop press! I have found that my venturi now does this job for me, see the Was it worth it section of the Venturi page for more details).

Effectively that drain pipe that tips over is a simple but effective method of emptying out the bottom of the big plant pot.

If you examine the pictures you will see that the white T-piece swirler pipes go through and below the plastic garden sieve. The garden sieve holds the filter media away from the bottom of the pot, and creates about a 2 inch space at the bottom of the bio-filter where all the crud can settle out into the bottom, and the circular swirling action of the incoming
water coming out of the swirler encourages the muck to go into the centre, and then gravity makes it settle out and go down the plug hole into the shower drain where it settles until I next empty the bio-filter. This works very well.

When I empty it, because the main drain pipe is a decent size bore, it means the water can really rush out fast, and this brings all the muck out very quickly. In the first few seconds first some slightly messy water comes out, followed quickly by a thick gloup of very dense messy water (fish crap, algae, small particles of blanket weed), then the water flows reasonably clear again.

Most times (perhaps every 2 or 3 days) I just empty out for a few seconds (with the pump still running because the swirling action helps clean out the bottom) so as not to lose too much water, whilst perhaps once a week I turn off the
pump and let it drain until no more water comes out (but of course like this several gallons of water are dumped, which sometimes requires a top-up in the pond).

This helps do a sort of reverse flushing action through the filter media. Then before I put the drain pipe upright again, I turn the pump back on, and let it swirl the last remaining crap out of the bottom, then raise the drain pipe back up and
clip it back into place, so it fills the bio-filter and operates normally.

This whole process can be done very quickly. 5 to 20 seconds for a part flush, and maybe 5 minutes for a full flush while you turn off the pump, empty the contents into a bucket to fertilise your garden, turn the pump back on and refill the bio-

I flush out the settlement chamber via the main drain into a bucket of water. One bucket is usually enough.

First I unclip the pipe, water starts to overflow.

Next I rotate the pipe forward and it empties into a bucket or on the garden. (Note that I have flipped the P-trap the other way around to that shown in the pictures at the head of this page, so as to allow complete emptying of the water out of the bio-filter).
Only once in a years use has the pipework accidentally slipped out of the bottom drain.

The biological media in the main bio-filter should only be removed and cleaned if it really needs it (i.e. if it has too much build-up of solid waste on it, perhaps just once at the start of the year - don't mistake this for healthy looking good bacteria gunk! You'll get to know the difference), and this should always be done in a bucket of the pond water. Changing too much water and cleaning too much of your biofilter will kill a lot of the bacteria resulting in yet more phytoplankton and green water. Once set up, leave it alone!

Under no circumstances should you clean the biological media of the bio-filter using water from your garden hose! It is also advisable not to clean the mechanical "waste solids" pre-filter with tap water for the same reason;

The low temperature and chlorine content of tap water will kill off the nitrifying bacteria of the bio-filter, leading to severe water quality problems. The bio-filter will be dead and will have to start its maturing process all over again.

If you need to top up your pond water-level, also use a de-chlorinating agent available from your fish pond supplier (I use "Fresh Start").


Conclusion and finally the Venturi

That completes the construction of the main bio-filter.

Three very important things when you have finished building the bio-filter:

1. Prime the filter itself with some bacteria as explained earlier. During the first few weeks it won't hurt to re-prime with more fresh bacteria every week or two. Just follow the directions on the packet/bottle.

2. I recommend adding a new dose of bacteria on a monthly basis throughout the year. This will boost any natural dying-off of the bacteria, and help renew any culture loss as a result of the cleaning cycle, topping up the pond with tap water and so on.

3. You MUST be patient. You can expect the water to start to look cleaner due to solids filtration within a couple of days, gradually clearing over a couple of weeks, but the biological effect to clear the green water will take considerably longer, anything from 3 to 8 weeks depending on conditions. This would be exactly the same even if you had bought and installed an off-the-shelf unit.

It will take anything from 6 to 8 weeks to fully mature and become effective, and Skippy's say the cycling of the various processes may result in the green water going away, then re-appearing a couple of times.

One thing I have strictly adhered to is not to put any commercial algae reducing solutions into the pond.
Neither green-water nor blanket-weed control solutions (other than some barley straw which is a natural solution). I want to see exactly how well the bio-filter works, without any assistance other than natural processes, and plants. Also as mentioned earlier the UVC lamp in the Bio-Force is not connected, so also has no effect on the final results.

During the first couple of weeks after building my filter, not a lot happened. It was still pea-green and murky. I think this was partly due to the various modifications and tweaks I was making here and there, stopping/starting the system, pulling it apart, then putting it back together again, coupled with a lot of disturbance to the planting and cleaning out blanket weed by hand, which in itself causes sediment to cloud up the water.

The fish love it when I get my shirt off, and I reach right deep into the pond and dig around with my hands. They have got quite used to this behaviour from me, and come right up between my hands, looking to see what grub I might have disturbed from the bottom and sides.

I really needed to just leave the pond and filter to settle down, but with the pump and pre-filter needing constant attention I just kept on messing around with it. For the first couple of weeks the pre-filter needed constant cleaning out.

It wasn't until I added the Venturi that suddenly everything started to happen.........

So the next step is to show you the venturi.

If you have any comments or suggestions about this project please contact me:

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